全文获取类型
收费全文 | 205篇 |
免费 | 11篇 |
专业分类
林业 | 14篇 |
农学 | 8篇 |
基础科学 | 3篇 |
58篇 | |
综合类 | 23篇 |
农作物 | 9篇 |
水产渔业 | 20篇 |
畜牧兽医 | 43篇 |
园艺 | 3篇 |
植物保护 | 35篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 1篇 |
2013年 | 6篇 |
2012年 | 11篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 21篇 |
2007年 | 16篇 |
2006年 | 9篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 15篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1955年 | 1篇 |
1870年 | 1篇 |
排序方式: 共有216条查询结果,搜索用时 15 毫秒
101.
Lauer P Rinaudo CD Soriani M Margarit I Maione D Rosini R Taddei AR Mora M Rappuoli R Grandi G Telford JL 《Science (New York, N.Y.)》2005,309(5731):105
Pili are essential virulence factors in many Gram-negative bacteria; however, they have not been described in most important Gram-positive pathogens. While screening the sequence of multiple genomes of Group B Streptococcus, we identified protective antigens that formed high molecular weight polymers. Immunogold electron microscopy revealed that the structures have a pilus-like form. These large structures have gone unrecognized in decades of studies of Group B Streptococcus. 相似文献
102.
Adrenergic Regulation of Lipid Mobilization in Fishes; a Possible Role in Hypoxia Survival 总被引:1,自引:0,他引:1
Guido van den Thillart Gerjanne Vianen Johan Zaagsma 《Fish physiology and biochemistry》2002,27(3-4):189-204
Lipids are for fish the major energy source. The nutritional conditions of most species vary throughout the year considerably. Thus storage and mobilization of lipids have to be tightly controlled, yet little is known about its control. Though several hormones are known to have a lipolytic effect, short term regulation of lipolysis is known for catecholamines only. Catecholamines are usually released under stress conditions, including hypoxia. In mammals these hormones have a strong lipolytic action, causing high plasma fatty acids levels during hypoxia. In contrast to mammals, several fish species show a decrease of plasma FFA-levels during hypoxia and anoxia. However, some studies gave contrasting results when catecholamines were administrated to different fish species. The reason for this may be due to opposing effects of catecholamines on lipolysis in different tissues. From catecholamine administration experiments in cannulated carp there is evidence that norepinephrine inhibits lipolysis via β1- and β3- adrenoceptors while β2-adrenoceptors are involved in stimulation of lipolysis. Thus the opposite responses of different β-adrenoceptors may explain the conflicting in-vivo results obtained with fish. In vitro studies with adipocytes from different fish species confirm that activation of β-adrenoceptors suppresses lipolysis, while the opposite occurs in hepatocytes. Inhibiting β1- and β3- adrenoceptors in adipocytes were shown to be involved. Under hypoxia β-oxidation is inhibited, resulting in accumulation of fatty acids together with intermediates of the β-oxidation. This process may cause severe cellular damage in mammalian tissues, which ‘apparently’ does not occur in fishes. Fishes encounter (environmental) hypoxia on a regular basis, while for mammals hypoxia/anoxia is a pathological phenomenon. Hence the suppression of lipolysis in fishes under hypoxia (by β1- and β3- adrenoceptors) may be considered as a survival mechanism lost in higher vertebrates. 相似文献
103.
Divine Foundjem-Tita Zac Tchoundjeu Stijn Speelman Marijke D’Haese Ann Degrande Ebenezer Asaah Guido van Huylenbroeck Patrick van Damme Ousseynou Ndoye 《Small-Scale Forestry》2013,12(3):489-505
Agroforestry and planting trees on farmers’ fields have been reported as important elements in a strategy to meet the millennium development goals of poverty reduction and climate change improvement. However, their uptake seems to be constrained by factors both internal and external to the household and related to the policy and legislative environment. This paper examines the impact of these factors on farmers’ decisions to plant trees. Cameroon is used as a case to analyse whether existing policies and legislation governing trees support or discourage tree planting, using qualitative content analyses. Although their mission papers and statements suggest most national government policies in Cameroon address tree planting and agroforestry, actual legislation designed to follow up the policies mostly contradicts the poverty reduction goals. Often legislation and regulations are more conservation-oriented and do not provide a clear procedure to distinguish between products from trees found in the wild and those gathered from farmers’ fields. 相似文献
104.
Veerle Mommaerts Kurt Put Jessica Vandeven Kris Jans Guido Sterk Lucien Hoffmann Guy Smagghe 《Pest management science》2010,66(11):1199-1207
BACKGROUND: To date, in modern agriculture, biological control strategies are increasingly becoming the preferred pest management approach. However, the success of microbiological control agents (MCAs) largely depends on efficient dissemination into the crop. The pollinator‐and‐vector technology employs pollinating insects like bees for a better dissemination. In this study, a new dispenser for bumblebee workers of Bombus terrestris L. was developed. Binab‐T‐vector and Prestop‐Mix were used as two typical MCA products for dissemination. RESULTS: In a first series of experiments in the laboratory for optimisation, the newly developed dispenser was a two‐way type dispenser, 20 cm long, with two rectangular compartments and different entrance and exit holes. In addition, the amounts of MCA loaded on the workers were 10 times higher with the new dispenser as compared with the side‐by‐side passageway (SSP) dispenser. Typically, the highest amounts were recovered from the thorax and legs of the workers. In a second series of experiments under greenhouse conditions with the use of queen‐right B. terrestris hives, successful dissemination in strawberry flowers was obtained at different distances from the hive (0–8 m, 8–18 m and 18–21 m), and the workers inoculated the first, second and third flowers that were consecutively visited. In addition, the new dispenser caused no adverse effects on worker foraging intensity, whereas a dramatic reduction was scored with an SSP dispenser. Finally, the data suggested that it is necessary to refill the newly developed dispenser at 3 day intervals. CONCLUSIONS: The results demonstrated that, with the use of the newly developed dispenser, bumblebee workers carried high amounts of MCA, and this resulted in a successful dissemination of MCA into strawberry flowers. Copyright © 2010 Society of Chemical Industry 相似文献
105.
Dalila Haouas Flamini Guido Ben Halima-Kamel Monia Ben Hamouda Mohamed Habib 《Industrial Crops and Products》2011,34(1):1128-1134
Compounds responsible for insecticidal properties of Chrysanthemum macrotum (D.R.) Ball. leaves against Spodoptera littoralis Boiduval caterpillars have been investigated. The screening of the insecticidal activity was performed by incorporating methanol, buthanol or ethyl acetate extracts, or some chromatographic fractions to the caterpillars’ artificial diet. It was noted that extracts and fractions ameliorated or disturbed nutritional indexes, being not always toxic for caterpillars. Among the tested fractions, one pure compound with a high insecticidal activity (percentage of mortality 66.7%) was purified. The nuclear magnetic resonance study allowed its identification as a polyacetylene derivative, in particular a spiroketal enol ether one. 相似文献
106.
BACKGROUND: Management of demethylation inhibitor (DMI) fungicide resistance in Monilinia fructicola (G. Winter) Honey is a priority in peach orchards of the southeastern United States, but DMI fungicides are still an important component of antiresistance strategies in view of the few effective alternatives. The goal of this study was to investigate potential benefits of a sulfur/propiconazole mixture for the control of propiconazole-resistant isolates.RESULTS: The mixture provided the best control for propiconazole-resistant isolates, regardless of protective or curative application timings, or the presence or absence of fruit injury. Propiconazole-resistant isolates developed disease on detached fruit after protective or curative applications of propiconazole or its mixture with sulfur, but protective applications of the mixture significantly reduced (P = 0.05) disease symptoms compared with the individual compounds. Additive to slightly synergistic effects were observed for the mixture in protective treatments of peaches inoculated with propiconazole-resistant isolates.CONCLUSION: The results suggest that the addition of elemental sulfur to a DMI fungicide is likely to be a relatively inexpensive means to improve brown rot control in peach production areas where reduced sensitivity to DMI fungicides is suspected but has not led to noticeable control failure. 相似文献
107.
108.
Alessandra Andrisani Gabriella Donà Elena Tibaldi Anna Maria Brunati Chiara Sabbadin Decio Armanini Gualtiero Alvisi Salvatore Gizzo Guido Ambrosini Eugenio Ragazzi Luciana Bordin 《Marine drugs》2015,13(9):5533-5551
Astaxanthin (Asta), a photo-protective red pigment of the carotenoid family, is known for its multiple beneficial properties. In this study, the effects of Asta on isolated human sperm were evaluated. Capacitation involves a series of transformations to let sperm acquire the correct features for potential oocyte fertilization, including the generation of a controlled amount of reactive oxygen species (ROS), cholesterol depletion of the sperm outer membrane, and protein tyrosine phosphorylation (Tyr-P) process in the head region. Volunteers, with normal spermiogram values, were divided in two separate groups on the basis of their ability to generate the correct content of endogenous ROS. Both patient group (PG) and control group (CG) were analysed for Tyr-phosphorylation (Tyr-P) pattern and percentages of acrosome-reacted cells (ARC) and non-viable cells (NVC), in the presence or absence of Asta. In addition, the involvement of ROS on membrane reorganization and the presence of Lyn, a Src family kinase associated with lipid rafts, were investigated. Results show that Lyn is present in the membranes of human sperm, mainly confined in midpiece in resting conditions. Following capacitation, Lyn translocated to the head concomitantly with raft relocation, thus allowing the Tyr-P of head proteins. Asta succeeded to trigger Lyn translocation in PG sperm thus bypassing the impaired ROS-related mechanism for rafts and Lyn translocation. In this study, we showed an interdependence between ROS generation and lipid rafts and Lyn relocation leading the cells to undergo the successive acrosome reaction (AR). Asta, by ameliorating PG sperm functioning, may be utilised to decrease male idiopathic infertility. 相似文献
109.
The majority of bioactive principles in a complex matrix such as natural products and botanical medicines are secondary rather than primary metabolites. In addition to being chemically diverse, the bioactivity of an ethnobotanical can comprise from one to several bioactive compounds, present in a complex mixture. Conventional discovery efforts utilize bioassay-guided fractionation (BGF) to isolate individual active compounds. When applied to complex natural products, BGF is often challenged by an apparent loss of activity during fractionation, resulting in weakly active isolated compounds. Metabolomic analysis can potentially complement existing the BGF paradigm by capturing the chemical complexity of the metabolites. The proposed biochemometric approach establishes a link between the chemistry of a secondary metabolome and a deserved health impact, using a high-throughput, high-resolution capable biological endpoint. The proof of principle is demonstrated for the anti-tuberculosis (TB) activity of the Alaskan ethnobotanical, Oplopanax horridus. Biochemometric analysis identified the 100 most active constituents from thousands of metabolites in the active extract by means of 2D orthogonal chromatography using countercurrent and GC-MS methods. Previously isolated O. horridus phytoconstituents were used as reference markers of known structure and bio (in)activity. Positive correlations allowed distinction of anti-TB actives from inactive compounds. A total of 29 bioactives from 3 main structural classes were assigned based on MS data. Biochemometric analysis is a new tool for the standardization of herbal medicines and ethnobotanicals, as well as for drug discovery from nature. The method can assign multiple active compounds in complex mixtures without their prior isolation or structure elucidation, while still providing an interface to structural information. 相似文献
110.
Dalila Haouas Pier Luigi Cioni Monia Ben Halima-Kamel Guido Flamini Mohamed Habib Ben Hamouda 《Journal of pest science》2012,85(3):367-379
Essential oils from three species of Chrysanthemum growing in Tunisia (C. coronarium, C. fuscatum, and C. grandiflorum) were first analyzed by gas chromatography (GC) and GC/mass spectrometry (MS) and then evaluated for toxicity and antifeeding action against Tribolium confusum. The essential oils obtained from leaves and flowers shared a similar qualitative composition, but the relative proportions of the constituents were quite different. The essential oil of C. grandiflorum was rich in sesquiterpenoids, while those of C. fuscatum and C. coronarium were rich in monoterpenoids. The main common constituents of all the essential oils were ??-pinene, myrcene, ??-humulene, ??-caryophylene, spathulenol, and caryophyllene oxide. The most effective essential oil was obtained from the leaves of C. grandiflorum, that inhibited the relative growth rate (?0.03?mg/mg/d), efficiency of conversion of ingested food (?50.69%), relative consumption rate, caused an antifeeding effect (66.43%) and a high mortality (80%) of T. confusum larvae. Topical application C. grandiflorum essential oil caused a significant insect mortality that attends 27% after 7?days of treatment. While essential oil from C. coronarium flowers has contact and fumigant toxicity with a mortality of 9 and 13%, respectively. Results analysis highlights a relationship between essential oils composition and insecticidal activity against T. confusum. The study showed that each essential oil has specific chemical composition and act differently according to the nature of attributed test. The use of essential oils from different Chrysanthemum species with different methods helps poor farmers who store small amounts of grains to preserve it against pest infestation. 相似文献